We now expect our snacks to protect us against our own foibles, and some snacks are able to oblige us.

You could say America is in the midst of a food revolution. Again. The first time around, we went from both ends of the spectrum—haute cuisine and meat-and-potatoes—to food that was not only fresher and lighter but inventive in its presentation. Do we need to mention healthier?

Today, we want foods to provide not just nutrients but protection against human frailties. We demand foods that fill us up and curb our appetites at the same time—with minimal calories—and shield us from cancer and other disease.

We want even our snacks to perform for us. According to the Institute of Food Technologists, 66 percent of all consumers want snacks with more nutrition, and 63 percent want them with fewer calories.

In response, the American food industry is intent on providing "smart treats." What "smart" mostly means is food packaged in units of 100 calories or less, says Roger Clemens, professor of food science at the University of Southern California.

He believes today's ideal snack is a product of new food technologies, like fruits and veggies dried to a manageable medium between hard leather and slurpy succulence. "It's too messy to eat a regular peach while driving your car," he says, "but new low-moisture packaging with a built-in antimicrobial layer can help people enjoy" a nutritious peach.

And the individual packaging will automatically help people reduce portion size, right? That's the theory.

But two studies reported in the Journal of Consumer Research suggest that we have ways of outsmarting even the smartest of treats. A team of Dutch and Portuguese researchers found that small packages encourage people to consume more calories: They make people particularly likely to give into temptation in the first place. By contrast, large packages activate people's dieting concerns, says an Arizona State University team; they tend to prompt eaters to think twice before opening and diving in.

The solution is not to wage war against snacking, says Brian Wansink, author of Mindless Eating and head of the USDA's Center for Nutrition Policy and Promotion. What really drives snacking is our need for compensation. We reward ourselves for doing something difficult, like exercise or having a bad day watching the kids.

Wansink's list of smart snacks begins with high-protein food like a handful of nuts or a glass of low-fat milk. Tomato juice works, as do fresh fruits and cut veggies.

Even smarter is to substitute an alternative behavior, like going for a walk. Smartest of all, he insists, is drinking a glass of water. "We often confuse dehydration for hunger." —Hara Estroff Marano